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<title>Struct template default_eval</title>
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<div class="refentry">
<a name="boost.proto.context.default_eval"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Struct template default_eval</span></h2>
<p>boost::proto::context::default_eval &#8212; 
            A BinaryFunction that accepts a Proto expression and a context, evaluates
            each child expression with the context, and combines the result using the
            standard C++ meaning for the operator represented by the current expression
            node.
          </p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../../proto/reference.html#header.boost.proto.context.default_hpp" title="Header &lt;boost/proto/context/default.hpp&gt;">boost/proto/context/default.hpp</a>&gt;

</span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <a class="link" href="../../../Expr.html" title="Concept Expr">Expr</a><span class="special">,</span> <span class="keyword">typename</span> Context<span class="special">&gt;</span> 
<span class="keyword">struct</span> <a class="link" href="default_eval.html" title="Struct template default_eval">default_eval</a> <span class="special">{</span>
  <span class="comment">// <a class="link" href="default_eval.html#boost.proto.context.default_evaltypes">types</a></span>
  <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">::</span><span class="identifier">tag_type</span> <a name="boost.proto.context.default_eval.Tag"></a><span class="identifier">Tag</span><span class="special">;</span>          <span class="comment">// For exposition only</span>
  <span class="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">see</span><span class="special">-</span><span class="identifier">below</span></em></span>               <a class="link" href="default_eval.html#boost.proto.context.default_eval.result_type"><span class="identifier">result_type</span></a><span class="special">;</span>

  <span class="comment">// <a class="link" href="default_eval.html#idp91786608-bb">public member functions</a></span>
  <span class="identifier">result_type</span> <a class="link" href="default_eval.html#idp91786896-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="identifier">Expr</span> <span class="special">&amp;</span><span class="special">,</span> <span class="identifier">Context</span> <span class="special">&amp;</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>

  <span class="comment">// public data members</span>
  <span class="keyword">static</span> <span class="identifier">Expr</span> <span class="special">&amp;</span> <span class="identifier">s_expr</span><span class="special">;</span>  <span class="comment">// For exposition only</span>
  <span class="keyword">static</span> <span class="identifier">Context</span> <span class="special">&amp;</span> <span class="identifier">s_context</span><span class="special">;</span>  <span class="comment">// For exposition only</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idp145249344"></a><h2>Description</h2>
<p>
              Let <code class="computeroutput"><code class="computeroutput">OP</code></code> be the C++ operator
              corresponding to <code class="computeroutput">Expr::proto_tag</code>. (For example, if
              <code class="computeroutput">Tag</code> is <code class="computeroutput">
              <a class="link" href="../tag/plus.html" title="Struct plus">proto::tag::plus</a></code>, let <code class="computeroutput">
              <code class="computeroutput">OP</code></code> be <code class="computeroutput">+</code>.)
            </p>
<p>
              The behavior of this class is specified in terms of the C++0x <code class="computeroutput">decltype</code>
              keyword. In systems where this keyword is not available, Proto uses the Boost.Typeof library to
              approximate the behavior.
            </p>
<div class="refsect2">
<a name="idp145253568"></a><h3>
<a name="boost.proto.context.default_evaltypes"></a><code class="computeroutput">default_eval</code> 
        public
       types</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<p>
<span class="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">see</span><span class="special">-</span><span class="identifier">below</span></em></span> <a name="boost.proto.context.default_eval.result_type"></a><span class="identifier">result_type</span><span class="special">;</span></p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> corresponds to a unary prefix operator,
                    then the result type is
                    </p>
<pre class="programlisting"><span class="identifier">decltype</span><span class="special">(</span>
  <span class="identifier">OP</span> <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_idp90963568.html" title="Function child">proto::child</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span>
<span class="special">)</span></pre>
<p>
                  </p>
</li>
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> corresponds to a unary postfix operator,
                    then the result type is
                    </p>
<pre class="programlisting"><span class="identifier">decltype</span><span class="special">(</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_idp90963568.html" title="Function child">proto::child</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="identifier">OP</span>
<span class="special">)</span></pre>
<p>
                  </p>
</li>
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> corresponds to a binary infix operator,
                    then the result type is
                    </p>
<pre class="programlisting"><span class="identifier">decltype</span><span class="special">(</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../left_idp90994144.html" title="Function left">proto::left</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="identifier">OP</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../right_idp91001552.html" title="Function right">proto::right</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span>
<span class="special">)</span></pre>
<p>
                  </p>
</li>
<li class="listitem">
<p>
                  If <code class="computeroutput">Tag</code> is <code class="computeroutput">
                    <a class="link" href="../tag/subscript.html" title="Struct subscript">proto::tag::subscript</a>
                  </code>,
                  then the result type is
                  </p>
<pre class="programlisting"><span class="identifier">decltype</span><span class="special">(</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../left_idp90994144.html" title="Function left">proto::left</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">[</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../right_idp91001552.html" title="Function right">proto::right</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">]</span>
<span class="special">)</span></pre>
<p>
                </p>
</li>
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> is <code class="computeroutput">
                      <a class="link" href="../tag/if_else_.html" title="Struct if_else_">proto::tag::if_else_</a>
                    </code>,
                    then the result type is
                    </p>
<pre class="programlisting"><span class="identifier">decltype</span><span class="special">(</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;</span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">?</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;</span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">:</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a><span class="special">&lt;</span><span class="number">2</span><span class="special">&gt;</span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span>
<span class="special">)</span></pre>
<p>
                  </p>
</li>
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> is <code class="computeroutput">
                      <a class="link" href="../tag/function.html" title="Struct function">proto::tag::function</a>
                    </code>,
                    then the result type is
                    </p>
<pre class="programlisting"><span class="identifier">decltype</span><span class="special">(</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;</span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">(</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;</span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span><span class="special">,</span>
  <span class="special">...</span>
  <a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a><span class="special">&lt;</span><span class="identifier">N</span><span class="special">&gt;</span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">)</span>
<span class="special">)</span></pre>
<p>
                  </p>
</li>
</ul></div>
</li></ol></div>
</div>
<div class="refsect2">
<a name="idp145311712"></a><h3>
<a name="idp91786608-bb"></a><code class="computeroutput">default_eval</code> public member functions</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><span class="identifier">result_type</span> <a name="idp91786896-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">Expr</span> <span class="special">&amp;</span> expr<span class="special">,</span> <span class="identifier">Context</span> <span class="special">&amp;</span> context<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> corresponds to a unary prefix operator,
                    then return
                    </p>
<pre class="programlisting">OP <code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_idp90963568.html" title="Function child">proto::child</a></code>(expr), context)</pre>
<p>
                  </p>
</li>
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> corresponds to a unary postfix operator,
                    then return
                    </p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_idp90963568.html" title="Function child">proto::child</a></code>(expr), context) OP</pre>
<p>
                  </p>
</li>
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> corresponds to a binary infix operator,
                    then return
                    </p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../left_idp90994144.html" title="Function left">proto::left</a></code>(expr), context) OP
<code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../right_idp91001552.html" title="Function right">proto::right</a></code>(expr), context)</pre>
<p>
                  </p>
</li>
<li class="listitem">
<p>
                  If <code class="computeroutput">Tag</code> is <code class="computeroutput">
                    <code class="computeroutput"><a class="link" href="../tag/subscript.html" title="Struct subscript">proto::tag::subscript</a></code>
                  </code>,
                  then return
                  </p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../left_idp90994144.html" title="Function left">proto::left</a></code>(expr), context) [
<code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../right_idp91001552.html" title="Function right">proto::right</a></code>(expr), context) ]</pre>
<p>
                </p>
</li>
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> is <code class="computeroutput">
                      <code class="computeroutput"><a class="link" href="../tag/if_else_.html" title="Struct if_else_">proto::tag::if_else_</a></code>
                    </code>,
                    then return
                    </p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a></code>&lt;0&gt;(expr), context) ?
<code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a></code>&lt;1&gt;(expr), context) :
<code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a></code>&lt;2&gt;(expr), context)</pre>
<p>
                  </p>
</li>
<li class="listitem">
<p>
                    If <code class="computeroutput">Tag</code> is <code class="computeroutput">
                      <code class="computeroutput"><a class="link" href="../tag/function.html" title="Struct function">proto::tag::function</a></code>
                    </code>,
                    then return
                    </p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a></code>&lt;0&gt;(expr), context) (
<code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a></code>&lt;1&gt;(expr), context),
...
<code class="computeroutput"><a class="link" href="../eval_idp88899728.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idp90978080.html" title="Function child_c">proto::child_c</a></code>&lt;N&gt;(expr), context) )</pre>
<p>
                  </p>
</li>
</ul></div>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><code class="computeroutput">context</code></span></p></td>
<td><p>The evaluation context </p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">expr</code></span></p></td>
<td><p>The current expression </p></td>
</tr>
</tbody>
</table></div></td>
</tr></tbody>
</table></div>
</li></ol></div>
</div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2008 Eric Niebler<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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